System of broadcasting



May 24, 1932. E. s. PURINGTON 1,859,465

SYSTEM OF BROADCASTING Filed Oct. 22, 1928 E J Ll 11 7 II III In INVENTOR E ISON S PURINGTON BY J TORNEY Patented May 24, 1932 "fr a ELLISON s. PURINGTON, or GLOUCESTER, MAssAoHusErrsQAssrenoR 'ro JOHI\T I-IA.YS

HAMMOND, JR. a:

SYSTEM OF BROADCASTING Application filed October 22, 1828. Serial No. 314,047.

This invention relates to the transmission of intelligence by radiant energy and to systems of broadcasting information, music, etc. and more particularly to a system for permitting the broadcasting of a plurality of such programs without undue interference.

One object of this invention is to-provide a system of broadcasting in which the interference between a number of broadcasting stations operating at or near the same frequency may be prevented.

Another object of my invention is to economize in the amount of power necessary to broadcast a given number of radio programs by a plurality of radio broadcasting stations.

A further object of my invention is to accomplish with ease and accuracy the control of the carrier frequency being transmitted by a plurality of radio broadcasting stations. Further objects of my invention will appear from the following description taken in connection with the accompanying drawings.

In multiplexing of radio telephone or radio broadcast signals, the number of programs which can be handled within certain wave band limits are necessarily limited, and the accuracyof the frequencies used by each of the various transmitters is of extreme importance. It is an object of this invention to secure a big advantage in the transmission of a plurality of radio broadcast stations by increasing the number of communication channels possible, first by the accurate allocation of the signals and secondly by cutting down the amount of energy in the ether emanating from each of the radio transmitting stations. 7 7

As has previously been described and disclosed in connection with inventions of John Hays Hammond, Jr. and others, a single frequency may be used by broadcasting stations for the transmission of several independent messages by the use of double modulation. A difliculty, however, which arises in multiplexing of a plurality of radio broadcast programs over the same radio transmitter even though using the double modulation system is the interaction because of the load ings of one of the circuits with the other circuits.

Thus, a single antenna equipment of which 22.11

mon to a group of broadcast stations. There would be say one carrier frequency for. every five radio broadcast signals, and the amount of interference produced by the beating of the carrier waves of separate groups of transduced. A plurality of sub-stations, are provided one for each broadcast message that is to be transmitted, and equipped with suitable antennae. Suitable means are provided for supplying each of the sub-stations from. the central station with the carrier frequency, either by means of radio transmission and re ception in the sub-stations or by direct wire connection. Each of the sub-stationswould supplied by the central carrier station and after modulation would transmit one of the side bands produced, suppressing the carrier frequency, and remaining side band.

carrier frequencies by straight modulation system of course suppressing the carrier in its transmission and preferably also, one of the side bands.

ceived by supersonic frequencies different from each other and also modulate the supersonic frequencies by the audio frequency of the radio. program. Their transmission The remaining stations ,3

0 could modulate the carrier frequency re- V 05 mitters is correspondingly substantially rethen modulate with its program the frequency 8 One of the stations may operate upon the would comprise them-one ofthe side bands" produced by the supersonic frequency modulation of the carrier frequency. Or they each might modulate an independent high frequency by the audio frequency, transmitting one side band and suppressing the high" frequency and the other side band, in this case the independent high frequency being the same as one of the side bands which would be obtained by modulation of the carrier by ioo the supersonic frequency as given above.

Any other appropriate means may be used for producing the side band transmitted.

The carrier current may be furnished by an organization such as chamber of commerce, and the common wave in addition to use for'supplying carrier energy for-operation in connection with a sub-station may be used for continuous wave telegraphy by the shifting of the carrier waves slightly, say 500 cycles, without interfering with the proper functioning of the telephone channels.v This will provide for the supply of the carrier frequency with regard to the broad casting stations withoutadditional cost on thepart of the chamber of commerce or other centr-albody.

vI Iaving now briefly described my invention attention is invited to the accompanying drawings wherein Fig. 1 is a diagram'showing the general relationship of the broadcasting stations and the central station. Fig.

2 is a diagram showing the relationship between the frequencies of the broadcasting stations'and'the carrier frequency station of Fig. 1.

Referi-ingnow more-particularly to Fig. 1

there isshown at C a diagrammatic repre sentation of the central carrier frequency station such "as mightbe operated by the chamber of commerce. "This station as has been previously mentioned is'adapted to supply a continuouscarrier frequency of an output of say 100 k. W. For the sending of continuous frequency messages, this station might be provided with means for shifting the frequency of its transmission by a very slight amount which-however would be. sufiicient to operate upon a sensitive receiver of the type employed inlong distance transmission. broadcasting or sub-stations A, B and B the This station C will supply to the carrier frequency. The supply may be made either byineans of a telephone connection as indicated'by the lines connecting A, B and IE with .C, or ,may be by means of radio transmission in :the usual and well 'known .manner.

The sub-station A is provided with means 'forreceiving the incoming frequency from C.

and operating thereupon with its audio signalling currents to produce a radio side band with .the suppressed carrier of same frequency as G. Preferably one side band .only should be transmitted, with' the-other radio side band eliminated, Similarly substations B B etc. receive energy from O and operate thereupon to produce suitable side bands. 'Eachsub-station will have its own secondary frequency oscillator which serves to space the sub-station radiations correctly from the carrier .wave radiation. -Current of thesecondary frequency at each cub- .station will be modulated'by the audio signalling frequency in such a mannerthat the of the-, isual type.

current accurately spaced from frequency of the carrier station C by the agency of sec ondary frequency oscillators. For station A, this separation iszero, but for stationB ',B the separtions .will be difierent secondary frequencies suitably :chosen. Vvith station C used for-continuous wave telegraphy'by the 7 frequency shifting :i'nethod, 'the'suppressed carriers of all the sub-stations will correence s maintained. Thus, transmission of signals through any channel requires joint transmission'and reception from the, carrier station and a sub-station. I

The signalling strengths of thedifi'erent channels depend on the powers of the carrier wave station C and of the sub-stations. F or local work, for eXainple,the sub-station power might be very small, say watts, with a small antenna system, yet in combinationwith the carrier oflOO klwithe two are equivalent to a well modulated station of i For greater sigapproximately 500 watts. nalling strengths, the substations might have power-ratings ofl0'kilowatts,which in combination with the 100' kilowatt carrier: produce the equivalent of 50k'ilowatt stat-ions carrier frequency for several channels, the

equivalent of a-large number of efticientradio telephone stations may be attained, with a much smaller power, and much less possibilities of interferencethaii in the usual'arrangeinents of a separate carrier for each station.

It will be further seen that it 'willbepossible to give more exact control'to the carrier frequencies being used as the central stations only'would need be equipped with the expensive apparatus for accurately determin-' iiig the frequency. More exact control, is

.made possible also by centralizing the responsibility for. having the frequency correct.

quencies produced by the four stations of Fig. 1, clearly indicating the partwof the total which is produced by each station; The station C of Fig. 1 produces the'carrier frequency indicated at C in Fig. 2, the side bands A of- Fig. 2 are produced by'the broadcasting station A of Fig. 1, and the bands Bin'nd Thus, by using a single 1 In Fig.2 is shown a diagrani-repre' .senting the relative allocation of the frespondingly shift, so that the constant difi'er- 7 B are produced by the modulation at stations B and B respectively.

' In the receiver for receiving signals transmitted by sub stations B and B two detectors are provided. The first detector input circuit is tuned so as to receive energy from the carrier C and the desired radio side band. The output of the first detector is a secondary frequency side band corresponding to the sub-station selected. Further selectivity of signals is attained by selective amplification as in the superheterodyne arrangements. The amplified and purified secondary side bands are then reduced to audibility by the second detectorin combination with a suitable heterodyning secondary frequency.

i It will be apparent that various modifications of the above described systenrmay be constructed which will work equally well to carry out-the main idea involved.

Having thus described one embodiment of my invention, it is to be understood that the invention upon which this application is based is broader than the specific embodiment shown and described for the purpose of illustration and that, therefore, it is to be limited only by the scope of the following claims.

I claim:

1. The method of broadcasting a plurality of radio programs which comprises generating a current of a carrier frequency, transmitting said current, modulating said carrier frequency current by an audio frequency current, transmitting one of the side bands produced by said modulation to transmit one of the programs composing said broadcasting, producing a current of a band of frequencies by each of a plurality of audio frequency currents composing the remaining multiplex broadcast programs, spaced by different mean differences with respect to said carrier frequency current such that when said bands are transmitted and received they may be properly combined with said carrier frequency and distinguished from each other by means of double detection to reproduce each of said audio frequency currents, transmitting the bands thus produced, receiving at each of several localities one of the bands and the carrier frequency current thus transsaid carrier frequency by a small amount to send a code message, transmitting said carrier frequency current, modulating said carrier frequency current by an audio frequency current, transmitting one of the side bands produced by said modulation to transmit one of the programs composing said broadcasting, producing a current of a band of frequencies by each of a plurality of audio frequency currents, composing the remaining broadcast programs spaced by a difierent mean difference from said carrier frequency such that when said bands are transmitted and received they may be properly combined with said carrier frequency current and dis tinguished from each other by means of double detection to reproduce each of said audio frequencies, transmitting the bands thus produced at each of several localities, receiving one of the bands and the carrier frequency current thus transmitted, combining said bands and said carrier frequency current to reproduce each of said audio frequencies, and receiving said carrier frequency and detecting the variations in said carrier frequency to receive said code message.

3. The method of radio broadcasting a plurality of programs which comprises generating a carrier frequency wave, transmitting said wave, modulating said carrier frequency wave by an audio frequency current, transmitting one of the side bands produced by said modulation to transmit one of the programs composing said multiplex broadcast, producing a band of frequencies representative of each of a plurality of audio frequency currents composing the remaining multiplex broadcast programs such that when said bands are transmitted and received they may be properly combined with said carrier frequency wave and distinguished from each other by means of double detection to reproduce each of said audio frequency currents, and transmitting the bands thus produced.

4. The method of broadcasting a plurality of radio programs which comprises generating a carrier frequency wave, varying said carrier frequency by a small amount to send a code message, transmitting said carrier frequency wave, modulating said carrier frequency wave by an audio frequency current, transmitting one of the side bands produced by said modulation to transmit one of the programs composing said broadcasting, producing a band of frequencies representative of each of a plurality of audio frequency currents composing the remaining broadcast programs such that when said frequency bands are transmitted and received they may be properly combined with said carrier frequency and distinguished from each other by means of double detection to reproduce each of said audio frequency currents, and transmitting the frequency bands thus produced.

5. The method of broadcasting a plurality of radio programs which comprises generating a carrier frequency wave, transmitting said wave, producing a frequency band by each of a plurality of audio frequency currents composing the plural broadcast program such that when said bands are transmitted and .-received they m-ay abe combined .With'said carrier frequency; and distinguished from each otherto reproduce each of said audio frequency currents, transmitting the bands thus produced,-receiving at each .of a plurality of localities'one of the bands and the carrier frequency wave thus transmitted and combining said side bands and said carrier frequency to reproduce each'of said audio frequencies.

1,6. The method of broadcasting a plurality of radio programs which comprises generating a carrier frequency wave, varying said carrier frequency by a small amount to send a codemessage, transmitting said carrier frequency Wave, producing a frequency band by each of a plurality of audio-frequency Waves composing said plurality of broadcast ro rams such that when said fre uenc .Z) 7

bands are transmitted and received they may be combined with said carrier frequency Wave and distinguished from each other to reproduce each of said audio frequencies, transmitting the bands thus produced, at each of several localitiesreceiving ,one'of the frequency bands and the carrier wave, combining said side bandsand said carrier frequency to reproduce eachof said audio frequencies, and receiving said carrier frequency wave and detectingthe variations in the frequency of said Wave to reproduce said code message.

7 The method of radio broadcasting a pluralityof programs which comprises generating ,a current of a carrier frequency,

varying said frequency, broadcasting a band of frequencies representative of each of a plurality of audio frequency currents composing said broadcast programs such that 'when said bands-are transmitted and received they may be properly combined with sa1d carrier "frequency current and distinguished from each other to reproduce each of sa1d iaudio frequency currents, and transmitting the bands thus produced.

8. The method of radio broadcasting a plurality of programs which comprises generating a current of a carrier frequency, varying said carrier frequency by a small amount 1 to 1 send a code message, transmitting said carrier frequency current, producing a band of frequencies by each of a plurality of audio frequency currents composing the multiplex broadcast. programs, such that When-said bands are transmitted and received they may be properly combined with said carrier frequency current and distinguished from each other by means of double detection to reproduce each of said audio frequency currents, and transmitting the bands thus produced.

9. The method of radio broadcasting a :pluralityrof programs which comprises incle- .pendently,producing and transmitting a carrier frequency current, independently profrequency current differing from each other and from said carrier frequency current,

transmitting the. bands thus. produced, reeeiving ateach of aplurality ofo-stationsjsaidearrier-frequenoy current and one of said bands,

detecting the beat produced by double detection, and producing thereby an inter,- mediate beat frequency current, detecting said beat frequency and reproducing-theme by said audio frequency current. V a p 10. The method of signaling whichccomprises radiating a carrier wave fromcnestation common to a plurality of channelsaand radiating a ;plurality of bands accurately allocated with respect to said carrier wave and varying in frequency by an audio frequency representative of an audio signalfrom a plurality of other stations, and receiving conjointly the energy from said common carrler wave station and a selected band station.

11. The method ofbroadcasting a plurality of radio programs which comprises generating a carrier frequency wave, transmitting said wave, modulating said carrier frequency wave by an audlo frequenoy ourrentptransmitting one of the side bands produced by said modulation to transmit one of the programs composing said broadcasting, modulating a plurality of different intermediate frequency currents by each of the audiofre- :quency currents composing the :remaimng broadcast programs,anodulatmgsaid carrier frequency wave by one of :each of the. pairs of side bands thus produced,*transmitting :one of thefside bands produced by each tof' said last mentioned zmodulations ateach of several localities, receiving one of the side bands radiated and carrier frequency 'thus transmitted, and combiningrsaid side band .and said carrier frequency with the appropriate intermediate frequency energy .to IB- produce a desired on'e-of said audio frequencies.

12. The method of broadcasting .a'pluralityiof programs which comprises generating a carrier frequency Wave, varying the carrier frequency by :a small amount toisend a code message, transmltting sa1d carrier frequency Wave, modulatingsaid Wave by .an

audio frequency, transmitting one of ithe side modulating said carrier frequency wave by none of the side bands produced :by :eaohof said last mentioned modulations, transmitting I one -.of the side bands produced by ILL :last mentioned modulation ;.at .each of 'sevezal' i localities, receiving one of the side bands transmitted and the carrier frequency Wave transmitted, combining said side band and said carrier frequency Wave With an appropriate secondary frequency wave to reproduce each of the audio frequency currents, and receiving said carrier frequency Wave and detecting variations in said carrier frequency to receive said code message.

13. The method of broadcasting a plurality of radio programs which comprises generating a carrier frequency current, transmitting said current, modulating said current by an audio frequency current representative of one of the broadcasting programs being transmitted, transmitting one of the side bands produced by said modulation, producing currents of varying high carrier frequency varying in frequency by an amount 2 representative of the audio frequency current representative of each of the remaining programs being broadcast and difiering from said carrier frequency by a constant mean difference amount to transmit each of the remaining broadcast programs, transmitting the varying high frequency currents thus produced at each of several localities, receiving the carrier frequency current thus transmitted and one of the varying high frequency currents, combining said varying high frequency current and said carrier frequency current to reproduce the original audio frequency current representative of the various radio broadcasting programs. I

ELLISON S. PURINGTON. 

